Synthesis and Characterization of Cationic Hydrogels from Thiolated Copolymers for Independent Manipulation of Mechanical and Chemical Properties of Cell Substrates

Abstract

Cells sense both mechanical and chemical properties in their environment and respond to these inputs with altered phenotypes. Precise and selective experimental manipulations of these environmental cues require biocompatible synthetic materials, for which multiple properties can be fine‐tuned independently from each other. For example, cells typically show critical thresholds for cell adhesion as a function of substrate parameters such as stiffness and the degree of functionalization. However, the choice of tailor‐made, defined materials to produce such cell adhesion substrates is still very limited. Here, a platform of synthetic hydrogels based on well‐defined thiolated copolymers is presented. Therefore, four disulfide crosslinked hydrogels of different composition by free radical polymerization are prepared. After cleavage with dithiothreitol, four soluble copolymers P1–P4 with 0–96% cationic monomer content are obtained. P1 and P4 are then combined with PEGDA3500 as a crosslinker, to fabricate 12 hydrogels with variable elasticity, ranging from 8.1 to 26.3 kPa and cationic group concentrations of up to 350 µmol cm−3. Systematic analysis using COS7 cells shows that all of these hydrogels are nontoxic. However, successful cell adhesion requires both a minimal elasticity and a minimal cationic group concentration.

Concentration Dependent Effect of Quaternary Amines on the Adhesion of U251-MG Cells

“…The prepolymers were prepared by free radical polymerization and analyzed by proton nuclear magnetic resonance ( 1 H-NMR) spectroscopy, size-exclusion chromatography (SEC), and Ellman’s assay for thiol concentration [ 28 ]. For a detailed description of the polymer synthesis, we refer to a previous publication [ 25 ]. The monomers required for the synthesis of the polymers were inexpensive and could be prepared in a single synthesis step in large quantities.…”

“…The gelation time for all hydrogels were between 2 and 3 min independent of the concentration of cationic groups or RGD peptide. For a more detailed study of the gelation time, we refer to a previous study [ 25 ].…”

“…While neural cells prefer rather soft tissue, cells from the bones need a rather hard matrix [ 29 ]. The storage modulus could be adapted to the cells under investigation via the gel composition, the degree of crosslinking of the thiols, and the mass fraction used for gelation [ 25 ].…”

“…Therefore, well-defined synthetic materials with variable cationic group concentration should be helpful to better understand the effect of cationic charge density on cellular behavior. More recently, we have developed a hydrogel material where cationic group densities can be changed while keeping the stiffness and swelling behavior of the gel nearly constant [ 25 ].…”

Tailoring the Degradation Time of Polycationic PEG-Based Hydrogels toward Dynamic Cell Culture Matrices

“…16 Historically this was already exploited since the 1970s when Yavin and Yavin showed that the coating of cell culture dishes with poly(lysine) bearing an amino side group significantly enhances cell adhesion. 17 Since then, the integration of poly(lysine) into hydrogels has been widely exploited to enhance cell adhesion, 18,19 but also other polycations are used, such as poly(2-acryloyl trimethylammonium ethyl iodide) (PTMAEA) 20 or poly(2-(dimethyl amino)ethyl methacrylate) (PDMAEMA). 21,22 Once cells adhere to the synthetic hydrogel, proliferation, spreading, and migration are highly influenced by the mechanical properties of the scaffold.…”